The world is collectively engaged in a massive search for energy alternatives to ever higher priced crude oil. Among these alternatives, biodiesel has gained importance in recent years for its ability to mix with petroleum diesel. Biodiesel refers to a diesel-equivalent fuel consisting of short chain alkyl (methyl or ethyl) esters, made by transesterification of triglycerides, commonly known as vegetable oils or animal fats. The most common form uses methanol, the cheapest alcohol available, to produce methyl esters. The molecules in biodiesel are primarily fatty acid methyl ester (FAME), usually created by transesterification between fats and methanol. Currently, biodiesel is produced from various vegetable and plant oils.
One by-product of the transesterification process is glycerin (glycerol). For every 1 ton of biodiesel manufactured, 100 kg of glycerin is produced. Historically, there was a valuable market for the glycerin, which assisted the economics of the overall biodiesel process. With the increase in global biodiesel production, however, the by-product glycerin has saturated the market, which in turn has caused the market price of the crude glycerin to fall. The valuable disposition of this crude glycerin is vitally important to making the renewable biodiesel process more efficient in carbon utilization while offsetting production costs.
Glycerin usage is primarily used in foods and beverages, pharmaceutical and personal care, and fine chemicals. Glycerin is an oxygenated three carbon chemical. With the rapid expansion of biodiesel production, glycerin has become an abundant and inexpensive raw material. This character brings glycerin in as a potential chemical building block for other important renewable/green chemicals.
Two main classes of petrochemical raw materials are olefins (including ethylene and propylene) and aromatics (including benzene and xylene isomers), both of which are produced in very large quantities. They are the building blocks of chemicals and plastics we are using daily. These petroleum based commodity chemicals are not immune to resource limitation and increasing cost that we face in the fuel industry today. The search of alternative sources is vital important. The strategic development for technologies in bio-chemicals and process integration with biofuels could be similar to the current petroleum-based processes. The building block chemicals must be relatively easy and cheap to produce in large quantities. They should have chemical structures that facilitate their conversion into multiple products of commercial interest. Therefore, both bioethanol and glycerin have potential to be the building block chemicals for petroleum-based ethylene and propylene derivatives. The modernized biodiesel production enables the production of glycerin in large quantities at very low costs, which qualifies it for future development as one of the building block chemicals.
Propylene glycol is the preferred choice due to its established market and large consumption. One particularly interesting propylene glycol substitution is its use as a “green” non-toxic antifreeze and de-icing fluid. Propylene glycol is currently produced from petrochemical derived propylene. It has broad established market applications and potential for other applications. The successful conversion of glycerin to propylene glycol and the utilization of glycerin as a potential petrochemical feedstock shall positively impact the biodiesel business through better carbon utilization, by-product upgrade to high value products, opportunity to develop renewable chemicals, and maximum return on investment.